Composite biomaterials as artificial bone graft materials are pushing the present frontiers of bioengineering. In this study, a biomimetic, osteoconductive tricomposite scaffold made of hydroxyapatite (HA) embedded in non-mulberry Antheraea assama (A. assama) silk fibroin fibers and its fibroin solution is explored for its osteogenic potential. Scaffolds were physico-chemically characterized for morphology, porosity, secondary structure conformation, water retention ability, biodegradability, and mechanical property. The results revealed a ∼5-fold increase in scaffold compressive modulus on addition of HA and silk fibers to liquid silk as compared to pure silk scaffolds while maintaining high scaffold porosity (∼90%) with slower degradation rates. X-ray diffraction (XRD) results confirmed deposition of HA crystals on composite scaffolds. Furthermore, the crystallite size of HA within scaffolds was strongly regulated by the intrinsic physical cues of silk fibroin. Fourier transform infrared (FTIR) spectroscopy studies indicated strong interactions between HA and silk fibroin. The fabricated tricomposite scaffolds supported enhanced cellular viability and function (ALP activity) for both MG63 osteosarcoma and human bone marrow stem cells (hBMSCs) as compared to pure silk scaffolds without fiber or HA addition. In addition, higher expression of osteogenic gene markers such as collagen I (Col-I), osteocalcin (OCN), osteopontin (OPN), and bone sialoprotein (BSP) further substantiated the applicability of HA composite silk scaffolds for bone related applications. Immunostaining studies confirmed localization of Col-I and BSP and were in agreement with real-time gene expression results. These findings demonstrate the osteogenic potential of developed biodegradable tricomposite scaffolds with the added advantage of the affordability of its components as bone graft substitute materials.
Autologous graft replacement as a strategy to treat diseased peripheral small diameter (≤6 mm) blood vessel is often challenged by prior vein harvesting. To address this issue, we fabricated native-tissue mimicking multilayered small diameter vascular graft (SDVG) using mulberry (Bombyx mori) and Indian endemic non-mulberry (Antheraea assama and Philosamia ricini) silk. Patterned silk films were fabricated on microgrooved PDMS mold, casted by soft lithography. The biodegradable patterned film templates with aligned cell sheets were rolled onto an inert mandrel to mimic vascular conduit. The hemocompatible and mechanically strong non-mulberry films with RGD motif supported ∼1.2 folds greater proliferation of vascular cells with aligned anchorage. Elicitation of minimal immune response on subcutaneous implantation of the films in mice was complemented by ∼45% lower TNF α secretion by in vitro macrophage culture post 7 days. Pattern-induced alignment favored the functional contractile phenotype of smooth muscle cells (SMCs), expressing the signature markers-calponin, α-smooth muscle actin (α-SMA), and smooth muscle myosin heavy chain (SM-MHC). Endothelial cells (ECs) exhibited a typical punctuated pattern of von Willebrand factor (vWF). Deposition of collagen and elastin by the SMCs substantiated the aptness of the graft with desired biomechanical attributes. Furthermore, the burst strength of the fabricated conduit was in the range of ∼915-1260 mmHg, a prerequisite to withstand physiological pressure. This novel fabrication approach may eliminate the need of maturation in a pulsatile bioreactor for obtaining functional cellular phenotype. This work is thereby an attestation to the immense prospects of exploring non-mulberry silk for bioengineering a multilayered vascular conduit similar to a native vessel in "form and function", befitting for in vivo transplantation.
Silk,
a natural biopolymer, has been used clinically as suture
material over thousands of years and has received much impetus for
a plethora of biomedical applications in the last two decades. Silk
protein isolated from both mulberry and nonmulberry silkworm varieties
gained recognition as a potential biomaterial owing to its affordability
and remarkable physicochemical properties. Molecular studies on the
amino acid composition and conformation of silk proteins interpreted
in the present review provide a critical understanding of the difference
in crystallinity, hydrophobicity, and tensile strength among silkworm
silk proteins. Meticulous silk fibroin (SF) isolation procedures and
innovative processing techniques to fabricate gamut of two-dimensional
(2D) and three-dimensional (3D) matrices including the latest 3D printed
scaffolds have led SF for diverse biomedical applications. Crucial
factors for clinical success of any biomaterial, including biocompatibility,
immune response, and biodegradability, are discussed with particular
emphasis on the lesser-known endemic nonmulberry silk varieties, which
in recent years have gained considerable attention. The tunable biodegradation
and bioresorbable attributes of SF enabled its use in drug delivery
systems, thus proving it as an efficient and specific vehicle for
controlled drug release and targeted drug delivery. Advancements in
fabrication methodologies inspired biomedical researchers to develop
SF-based in vitro tissue models mimicking the spatiotemporal
arrangement and cellular distribution of native tissue. In
vitro tissue models own a unique demand for studying tissue
biology, cellular crosstalks, disease modeling, drug designing, and
high throughput drug screening applications. Significant progress
in silk biomaterial research has evolved into several silk-based healthcare
products in the market. Insights of silk-based products assessed in
the human clinical trials are presented in this review. Overall, the
current review explores the paradigm of the silk structure–function
relationship driving silk-based biomaterials toward tissue engineering,
drug delivery systems, and in vitro tissue models.
Materials
at the nanoscale offer numerous avenues to be explored
and exploited in diverse realms. Among others, proteinaceous biomaterials
such as silk hold immense prospects in the domain of nanoengineering.
Silk offers a unique combination of desirable facets like biocompatibility;
extraordinary mechanical properties, such as elongation, elasticity,
toughness, and modulus; and tunable biodegradability which are far
better than most naturally occurring and engineered materials. Much
of these properties are due to the molecular structure of the silk
protein and it is self-assembly into hierarchical structures. Taking
advantage of the hierarchical assembly, a large number of fabrication
strategies have now emerged that allow the tailoring of silk structure
of at the nanoscale. Harnessing the favorable properties of silk,
such methods offer a promising direction toward producing structurally
and functionally optimized silk nanomaterials. This review discusses
the critical structure–property relationship in silk that occurs
at the nanoscale and also aims to bring out the recent status in the
approaches for fabrication, characterization, and the gamut of applications
of various silk-based nanomaterials (nanoparticles, nanofibers, and
nanocomposites) in the niche of translational research. Harnessing
the favorable nanostructure of silk, the review also takes into account
the impetus of silk in avant-garde applications such
as chemo-biosensing, energy harvesting, microfluidics, and environmental
applications.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.